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    <title>31 Set实践</title>
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<body>
    <script>
        let arr = [1, 2, 3, 4, 5, 4, 3, 2, 1];
        // 1. 数组去重
        // let res = [...new Set(arr)];
        // console.log(res);

        // 2. 交集
        let arr2 = [4, 5, 6, 7];
        let s2 = new Set(arr2);
        // let result = [...new Set(arr)].filter(item => s2.has(item));
        // console.log(result);

        // 3. 并集
        // let union = [...new Set([...arr, ...arr2])];
        // console.log(union);

        // 4. 差集
        let diff = [...new Set(arr)].filter(item => ! s2.has(item));
        console.log(diff);
    </script>
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